One of the biggest criticisms about Silicon Valley is the lack of women.

Not enough female CEOs. Not enough female engineers. Not enough women on boards. Not enough women in venture capital. Not enough female entrepreneurs.

Yet by focusing on what’s missing, it’s easy to overlook what is here: a network of powerful women shaping the most important companies in Silicon Valley.

And so, for the first time, the Mercury News has compiled a list of the 10 most powerful women in the valley’s tech industry.

In putting this list together, what I found is that many of the most powerful women aren’t CEOs. They are second-in-commands, or leaders of major divisions. In fact, there is only one female CEO in the entire SV150: Yahoo’s Carol Bartz.

As such, their power is different, sometimes more subtle and often exercised behind the scenes.

Padmasree Warrior, one of the women on the list and chief technology officer of Cisco Systems, argues that women think of power and influence differently than men, and in a way that might be more suited to how technology and corporations are evolving in the 21st century.

“As a leader in a technology company, I know I have a lot of responsibility and power,” she said. “I’m always asking myself how I can give some of my power away to make others successful in the organization. I think men would look at it in a very different way.”

Of course, any such list is inherently subjective. I considered three factors in evaluating candidates: size of their company or organization; number of people under their management; and scope of their influence beyond their company.

Though in talking with Theresia Gouw Ranzetta, another one of the 10, I realized women might have their own way of defining power that’s very different from men.

“In terms of the word ‘power,’ most women I know don’t think of their influence in those terms,” said Ranzetta, a partner at venture capital firm Accel Partners. “They talk about wanting to do good, or wanting to build an organization, or helping others succeed, or having an impact on their community.”

Whatever words they might use to describe it, here are the 10 women I think wield the most power in Silicon Valley:

1. Safra Catz, 49, president, Oracle: Officially, Catz shares the title of president with Mark Hurd. But Catz is first among equals. A former investment banker, she was promoted to president in 2004 just as CEO Larry Ellison decided to consolidate the business software industry by buying other companies. Catz has largely been in charge of that campaign, which has transformed the industry and Oracle, now one of the world’s largest business software companies.

But Catz also must make these deals work, and she has. In addition, she oversees Oracle’s operations and is credited with giving the marching orders that have made divisions more efficient and profitable, without resorting to cost-cutting and layoffs that lesser managers might fall back on.

Catz provides consistent leadership at a company where the CEO, though larger than life, frequently disengages, spending weeks at a time at the America’s Cup or on his yacht in the Mediterranean. And no one doubts that Ellison hands her the keys when he’s gone.

For all those reasons, Catz is a clear choice as the most powerful woman in Silicon Valley.

2. Sheryl Sandberg, 41, chief operating officer, Facebook: If Sandberg sticks around long enough, she will give Catz a serious run for the No. 1 spot. Just not this year.

Sandberg arrived from Google in March 2008 just as Facebook was pivoting from wide-eyed startup to Internet power player. Her portfolio at Facebook includes sales, marketing, acquisitions, partnerships, human resources, public policy and communications. That essentially has left founder Mark Zuckerberg free to focus on the design of Facebook and cooking up new features.

Sandberg provided much-needed maturity to a company that had sometimes resembled a rowdy college dormitory. It was the adult supervision needed to help Facebook move from hot startup to Internet juggernaut. Thanks to Sandberg’s steady hand, Facebook raced past the 500 million-user mark even as it fought off a number of privacy controversies. It has become the most important company on the Web, an achievement that’s in no small part due to what she’s done since she arrived.

But why isn’t she the most powerful woman? While Facebook is a technology juggernaut, and a cultural force, it has not become an unstoppable business such as Oracle or Google.

That may all come in time, after its widely anticipated initial public offering. While Zuckerberg tinkers relentlessly with features and the user experience and the technology platform that makes it all work, it’s Sandberg who must capitalize on Facebook’s massive user base and make it the dominant Web business of the next decade.

3. Carol Bartz, 62, CEO, Yahoo: Why only No. 3? She does, after all, run what is still one of the largest networks of websites in the world.

That said, Bartz has increasingly become an object of derision, rather than respect, for her leadership. Since taking over Yahoo almost two years ago, she has operated with tremendous bluster but few clear results. Her tenure continues to be defined by what she’s gotten rid of: search business, employees, various product lines.

This would be defensible if Bartz did a better job of explaining where this takes Yahoo. But she hasn’t. And that isn’t a trivial matter. It has undermined the confidence of investors, who have left the stock at levels so low that it remains vulnerable to wild rumors of takeovers or buyouts.

The result is less discussion about what Yahoo will do next, and more speculation about how long Bartz will remain in charge. But given that Bartz is still the only CEO among the valley’s largest 150 public companies, her power remains substantial.

4. Ann Livermore, 52, executive vice president, Hewlett-Packard: Here may be one of the most confounding people on this list. More than anything, she is the ultimate survivor. She has been at HP since 1982, remarkable given the tidal wave of changes and the hundreds of thousands of layoffs over the past decade.

Livermore rose to become executive vice president of HP’s Enterprise Business, which accounts for almost half of the company’s revenue, under former CEO Carly Fiorina, stayed put under Mark Hurd, and is now reporting to her third CEO. If her unit, with its $57 billion in annual revenue, was its own company, it would be one of the largest tech companies in the world.

But her position may be in flux. Late Friday, The Wall Street Journal reported that HP may be splitting up her duties and adding her to the company’s board. Does that mean she’s moving up, down or sideways? Or like some other executives, could she even be on her way out? Stay tuned.

5. Marissa Mayer, 35, vice president of geographic and local services, Google: She was one of the first 20 employees at Google and is one of its highest-profile executives aside from the founders and CEO Eric Schmidt. And she has long been seen as the guardian of the search experience and the gatekeeper for new Google products.

This year, she got a new title that demonstrated the company’s commitment to local advertising. If Mayer can build this into a substantial new business for Google, she’s going to be getting a lot of headhunters calling about CEO openings — and if it’s a job in Silicon Valley she’ll rocket up this list.

6. Padmasree Warrior, 50, chief technology officer, Cisco Systems: Warrior made this list first for being one of the top executives at one of the valley’s largest and most important companies. That she isn’t even the first woman to occupy that job is a tribute to CEO John Chambers.

Warrior joined after being chief technology officer at Motorola for four years, where she gained an international reputation as one of the most influential women in technology. In fact, she was widely rumored to be a finalist to become President Barack Obama’s first chief technology officer. And with nearly 1.4 million followers on Twitter, only Mayer on this list can rival the way she regularly communicates with average people around the world.

7. Katie Cotton, 45, vice president, worldwide communications, Apple: Here is a woman who possesses the greatest of all superpowers: invisibility. Cotton oversees the most powerful mythmaking organization this side of Disney. Not only does she do a masterful job of stoking the cultlike fervor for Apple products, but she’s also considered to be the cultivator of Steve Jobs’ image, which just might be the most valuable commodity in Silicon Valley. And she does it all while rarely appearing in public, sending reporters e-mails or getting on the phone.

8. Susan Desmond-Hellmann, 53, chancellor, UC San Francisco: In the world of biotechnology and genetics, Desmond-Hellmann was already a towering figure. She played an instrumental role in developing some of the most important cancer-fighting drugs, and then spent years as president of Genentech.

But in August 2009, she became the first female chancellor at UC San Francisco, an often-overlooked institution despite being one of the region’s largest research organizations and the second-largest employer in San Francisco, with a $3 billion annual budget, 4,493 students and 22,196 employees. In her new role, she’s now also overseeing the development of UC San Francisco’s massive Mission Bay campus, which will include three medical and research facilities.

Her reputation in Silicon Valley is such that in her short tenure, she’s already landed a $1.5 million gift from Intel’s Andy Grove to create a new joint master’s degree program with UC Berkeley. And this summer, UC San Francisco nabbed a $100 million donation from Salesforce.com‘s Marc Benioff, who cited his confidence in Desmond-Hellmann’s leadership as one of the reasons for the contribution.

9. Theresia Gouw Ranzetta, 42, managing partner, Accel Partners: After almost two decades working as an entrepreneur and venture capitalist, Ranzetta has emerged as a significant player in the areas of e-commerce, social media and mobile investing. She’s been at Accel since 1999, where for many years she was the sole female VC partner before it recently added a second (based in London). In addition to sitting on the boards of eight companies, she’s become a mentor to countless female entrepreneurs and investors. And she’s been at the center of a powerful network of women in Silicon Valley that’s building support for female entrepreneurs.

10. Rep. Anna Eshoo, 68, D-Palo Alto: This may have been the single hardest call on this list. Silicon Valley is blessed with two excellent congresswomen: Eshoo, whose district stretches from Santa Cruz to San Francisco, and Rep. Zoe Lofgren of San Jose. Both advocate strongly on behalf of tech interests. And both are widely respected.

Asking people which woman ranked ahead of the other touched off some of the fiercest conversations I had in putting this list together.

That said, I gave the nod to Eshoo, who has been in the House since 1993, because she sits on two committees of vital interest to the valley: the House Energy and Commerce Committee and its subcommittee on Communications, Technology and the Internet. She’s been a longtime proponent of clean energy and innovation and also had a hand in helping some notable organizations in her district land some of the federal stimulus funding, including Tesla Motors.

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